FORMATION OF MACROCYCLIC POLY(OXYMETHYLENE) WITH NARROW MOLECULAR-WEIGHT DISTRIBUTION ON THE LAMELLAR CRYSTALS

Poly(oxymethylene) (POM) with a narrow molecular weight distribution was isolated by alkaline degradation of the bulk polymer, which was derived from 1,3,5-trioxane (TOX) under various cationic polymerization conditions. The isolated POM had no end groups (confirmed by XH NMR spectroscopic analysis) and was stable to both heat and alkali conditions, compared to ordinary POM. On the basis of these observations, it was concluded that the isolated POM had a macrocyclic structure. The number-average molecular weight of cyclic POM was in the 1300-2300 range, having a ratio of 1.1-1.2. The molecular weight of the cyclic POM increased with an increase in the thickness of the crystal lamellae of the original POM, and the calculated length of the cyclic POM was nearly equal to twice the thickness of the original POM crystal lamellae. These facts have been interpreted as meaning that the size of cyclic POM is determined by the lamellar thickness and that a macrocycle is formed by an intramolecular trans-acetalization on the surface of the crystal lamella. Cyclic POM underwent a further polyaddition reaction in the crystalline state upon the 7-ray irradiation. © 1990, American Chemical Society. All rights reserved.